#![feature(binary_heap_retain)]
use std::cmp::Ordering;
use std::collections::{BinaryHeap, VecDeque};
use std::time::{Duration, Instant};
#[derive(Debug, PartialEq, Eq)]
struct Event<T> {
    item: T,
    release_at: Instant,
}
impl<T: Eq> Ord for Event<T> {
    fn cmp(&self, other: &Self) -> Ordering {
        other.release_at.cmp(&self.release_at) // reverse ordering for min-heap
    }
}
impl<T: Eq> PartialOrd for Event<T> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}
#[derive(Debug, PartialEq)]
pub enum State<T> {
    Ready(T),
    Wait(Duration),
    Empty,
}
pub struct Debouncer<T> {
    events: BinaryHeap<Event<T>>,
}
impl<T: Eq> Debouncer<T> {
    pub fn new() -> Debouncer<T> {
        Debouncer {
            events: BinaryHeap::new(),
        }
    }
    pub fn put(&mut self, item: T, delay: Duration) {
        let time = Instant::now();
        self.events
            .retain(|e| e.release_at <= time || e.item != item);
        self.events.push(Event {
            item,
            release_at: time + delay,
        });
    }
    pub fn get(&mut self) -> State<T> {
        let time = Instant::now();
        match self.events.peek() {
            None => State::Empty,
            Some(e) if e.release_at > time => State::Wait(e.release_at - time),
            Some(_) => State::Ready(self.events.pop().unwrap().item),
        }
    }
}
pub struct UniformDebouncer<T> {
    delay: Duration,
    events: VecDeque<Event<T>>,
}
impl<T: PartialEq> UniformDebouncer<T> {
    pub fn new(delay: Duration) -> UniformDebouncer<T> {
        UniformDebouncer {
            delay,
            events: VecDeque::new(),
        }
    }
    pub fn put(&mut self, item: T) {
        let time = Instant::now();
        self.events
            .retain(|e| e.release_at <= time || e.item != item);
        self.events.push_back(Event {
            item,
            release_at: time + self.delay,
        });
    }
    pub fn get(&mut self) -> State<T> {
        let time = Instant::now();
        match self.events.get(0) {
            None => State::Empty,
            Some(e) if e.release_at > time => State::Wait(e.release_at - time),
            Some(_) => State::Ready(self.events.pop_front().unwrap().item),
        }
    }
}
#[cfg(test)]
mod tests {
    use super::*;
    use std::thread::sleep;
    use std::time::Duration;
    mod debouncer {
        use super::*;
        #[test]
        fn wait() {
            let mut debouncer = Debouncer::new();
            debouncer.put(1, Duration::from_millis(20));
            assert!(matches!(debouncer.get(), State::Wait(_)));
            sleep(Duration::from_millis(10));
            assert!(matches!(debouncer.get(), State::Wait(_)));
            sleep(Duration::from_millis(10));
            assert!(matches!(debouncer.get(), State::Ready(_)));
        }
        #[test]
        fn deduplication() {
            let mut debouncer = Debouncer::new();
            debouncer.put(1, Duration::from_millis(20));
            debouncer.put(2, Duration::from_millis(30));
            sleep(Duration::from_millis(10));
            debouncer.put(1, Duration::from_millis(10));
            sleep(Duration::from_millis(20));
            assert_eq!(
                vec![debouncer.get(), debouncer.get(), debouncer.get()],
                vec![State::Ready(1), State::Ready(2), State::Empty]
            );
        }
        #[test]
        fn event_order() {
            let mut debouncer = Debouncer::new();
            debouncer.put(2, Duration::from_millis(20));
            debouncer.put(1, Duration::from_millis(10));
            sleep(Duration::from_millis(30));
            assert_eq!(
                vec![debouncer.get(), debouncer.get()],
                vec![State::Ready(1), State::Ready(2)]
            );
        }
    }
    mod uniform_debouncer {
        use super::*;
        #[test]
        fn wait() {
            let mut debouncer = UniformDebouncer::new(Duration::from_millis(20));
            debouncer.put(1);
            assert!(matches!(debouncer.get(), State::Wait(_)));
            sleep(Duration::from_millis(10));
            assert!(matches!(debouncer.get(), State::Wait(_)));
            sleep(Duration::from_millis(10));
            assert!(matches!(debouncer.get(), State::Ready(_)));
        }
        #[test]
        fn deduplication() {
            let mut debouncer = UniformDebouncer::new(Duration::from_millis(20));
            debouncer.put(1);
            debouncer.put(2);
            sleep(Duration::from_millis(10));
            debouncer.put(1);
            sleep(Duration::from_millis(20));
            assert_eq!(
                vec![debouncer.get(), debouncer.get(), debouncer.get()],
                vec![State::Ready(2), State::Ready(1), State::Empty]
            );
        }
    }
}

Copyright (c) 2021 Ivan Sagalaev. All rights reserved.
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
3. Neither the name of the copyright holder nor the names of its contributors
may be used to endorse or promote products derived from this software without
specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

[package]
name = "debounce"
version = "0.1.0"
edition = "2018"
authors = ["Ivan Sagalaev <maniac@softwaremaniacs.org>"]
repository = "https://nest.pijul.com/isagalaev/debounce"
license = "BSD-3-Clause"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]

/target
Cargo.lock